1. Field of the Invention
This invention generally relates to scanning radio receivers and more particularly to signal-seeking radio receivers which automatically and sequentially scan a plurality of channels for tuning to predetermined radio frequencies, lock onto a tuned channel receiving a signal, and then automatically resume scanning upon termination of the received signal.
2. Description of the Prior Art
Scanning radio receivers which automatically and sequentially scan a plurality of channels for tuning to predetermined radio frequencies, lock onto a tuned channel receiving a signal, and upon termination of the received signal automatically resume the scan to locate another channel receiving a signal are now well known. Such a receiver is diclosed in U.S. Pat. No. 3,531,724, issued on Sept. 29, 1970, to George Fathauer and of common ownership herewith. This receiver employs semiconductor switching of crystals for determining the frequencies to which the receiver is tuned. These receivers gained immediate commercial acceptance and created the scanning radio receiver industry.
A scan delay feature has been incorporated into some commercially available scanning radio receivers. By actuating a scan delay switch, provided on these receivers, a user may cause the automatic resumption of the scan operation to be delayed for a period of time following termination of a signal on a receiving channel to enable the listener to hear a possible comeback communication if that channel is tuned to a frequency on which two-way communications occur. Such a receiver incorporating a scan delay circuit is disclosed in U.S. Pat. No. 3,824,475, issued on July 16, 1974, to Peter W. Pflasterer.
A major drawback in employing a scan delay circuit is that it causes a delay upon termination of each signal received on every channel, regardless of the mode of communication. Such delays on channels that are tuned to frequencies on which only one-way communications occur are needless since any possible comeback communication would be at a different frequency. These needless scan delays significantly increase the overall scan time thereby resulting in missed communications on other channels. For this reason, the conventional non-selective scan delay feature is highly undesirable and has not been uniformly adopted by the scanning radio industry.